Pentagon suspends F-35 flights due to crack in engine blade

All about the Pratt & Whitney F135 and the (cancelled) General Electric/Rolls-Royce F136
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maus92

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Unread post02 Mar 2013, 14:03

count_to_10 wrote:Looking at the videos of high AOA test, they don't seem at all interested in maintaining level flight.

It's too bad TEG hasn't been poking around here recently. I'm sure he could explain a lot.


Maybe they were exploring Vs1 in the vids you watched. Who knows...
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count_to_10

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Unread post02 Mar 2013, 15:41

maus92 wrote:
count_to_10 wrote:Looking at the videos of high AOA test, they don't seem at all interested in maintaining level flight.

It's too bad TEG hasn't been poking around here recently. I'm sure he could explain a lot.


Maybe they were exploring Vs1 in the vids you watched. Who knows...

Well, I don't.
On the other hand, high angle of attack is supposed to be only possible at low speeds anyway.
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Unread post02 Mar 2013, 18:54

Maintaining level flight during High AoA tests is not a requirement, and much of the time is not possible due to the low airspeeds.
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maus92

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Unread post02 Mar 2013, 19:51

I'm curious about other fighter engine programs that have experienced similar failures in similar test circumstances. Any recent examples come to mind?
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Unread post02 Mar 2013, 20:14

We haven't really built a new engine in the past decade. 414 is really almost 20 years old at this point.

But there shouldn't be that much difference between the Military and Civil design processes... and we've seen two catastrophic failures in the past three years: Trent 900 on A380s and GENx on the 787 (on aircraft that had been cleared in service after qualifications.) Its not that uncommon at all.
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Unread post03 Mar 2013, 02:52

maus92 wrote:
count_to_10 wrote:
f-22lm wrote:The engine for AF-02 has a little crack in the engine , but AF-04 (which is undertaking high AOA) doesn't. I wonder why? :?:

What about high AOA would stress the engine?
Particularly if the culprit is excess heat?


Higher thrust required to maintain level flight


AF-2 did the preponderance of the low altitude, high q (dynamic pressure) flights, which require lotsa time in AB.

The hi alpha work is above 30K feet, and the need in test is to stay on-condition for as long as possible -- not necessarily maintain level flight. Would be pretty tough to maintain level flight at 35K' at 100 KCAS or less at 50+alpha anyway.
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Unread post03 Mar 2013, 03:59

hb_pencil wrote:We haven't really built a new engine in the past decade. 414 is really almost 20 years old at this point.

But there shouldn't be that much difference between the Military and Civil design processes... and we've seen two catastrophic failures in the past three years: Trent 900 on A380s and GENx on the 787 (on aircraft that had been cleared in service after qualifications.) Its not that uncommon at all.


As are the EJ200 and M88 (~20 year old designs.) Gen 4/4.5 powerplants seem to be more or less trouble free vs. the F135 and the newer commercial designs you mention. A fair question then would be did any of the other "SDD" aircraft (Super Hornet, Eurofighter, Rafale) suffer similar engine faults at ~450 EFHs? If not, maybe those development aircraft were never stressed as often as AF-2, or maybe being twin-engined (and lower output) has something to do with it.
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Unread post05 Mar 2013, 22:19

F-35 Fan Blade Crack Raises F-35 Durability Questions
Amy Butler / Aviation Week

"A .6 in. crack in a third-stage low pressure turbine (LPT) blade of an F-35A last month was the result of “thermal creep,” says USAF Lt. Gen. Christopher Bogdan, F-35 program executive officer.

Though the problem is not thought to be a design flaw in the F135 engine, the Pratt & Whitney propulsion system is “not out of the woods” yet as officials study what implications there could be for durability of the system once it is fielded, he told an audience March 5 at Aviation Week’s Defense Technology & Affordability Requirements conference outside Washington."

"Two other aircraft in the conventional-takeoff-and-landing fleet, AF-3 and AF-6 remain grounded because they have been flown in similar – though not quite as rigorous – conditions."

"Engine experts will require at least two more weeks to explore what implications there are for engine durability, Bogdan says. “What level of thermal stress would it take to get to that point on a normal airplane,” not exposed to such extremes, he says. “The issue is if it turns out that it is less than 100% of what we expect the life of the engine to be, then we have turbine blade having life limiting parts on it and we’ll have to deal with that.”"

http://www.aviationweek.com/Blogs.aspx? ... 4a949858fd
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Unread post05 Mar 2013, 23:05

maus92 wrote:
hb_pencil wrote:We haven't really built a new engine in the past decade. 414 is really almost 20 years old at this point.

But there shouldn't be that much difference between the Military and Civil design processes... and we've seen two catastrophic failures in the past three years: Trent 900 on A380s and GENx on the 787 (on aircraft that had been cleared in service after qualifications.) Its not that uncommon at all.


As are the EJ200 and M88 (~20 year old designs.) Gen 4/4.5 powerplants seem to be more or less trouble free vs. the F135 and the newer commercial designs you mention. A fair question then would be did any of the other "SDD" aircraft (Super Hornet, Eurofighter, Rafale) suffer similar engine faults at ~450 EFHs? If not, maybe those development aircraft were never stressed as often as AF-2, or maybe being twin-engined (and lower output) has something to do with it.


Eurofighter did; they pulled all of the development engines after a 2002 crash in Spain and replaced them with newer models. I'm not aware of anything with the others, but that is probably because I did not pay attention to this stuff back then. I suspect the Rafale probably did, but it was never disclosed. I really don't think the F-35 (or other programs) are really as unique as you suggest.
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Unread post06 Mar 2013, 00:37

[quote="maus92..."A .6 in. crack in a third-stage low pressure turbine (LPT) blade of an F-35A last month was the result of “thermal creep,” says USAF Lt. Gen. Christopher Bogdan, ....

The F-135 was developed from the F-119 and the Raptor has flown many hours in high Alpha maneuvers, has "thermal creep" occured in the two stage turbine of the F-22? :?:
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Unread post06 Mar 2013, 01:42

maus92 wrote:...As are the EJ200 and M88 (~20 year old designs.) Gen 4/4.5 powerplants seem to be more or less trouble free vs. the F135 and the newer commercial designs you mention. A fair question then would be did any of the other "SDD" aircraft (Super Hornet, Eurofighter, Rafale) suffer similar engine faults at ~450 EFHs? If not, maybe those development aircraft were never stressed as often as AF-2, or maybe being twin-engined (and lower output) has something to do with it.


From the Baltimore Sun in 1998 -- "A series of engine problems -- such as occasional failures during flight and ground tests, excessive smoke, and extended warm-up time -- has delayed development up to eight months and increased costs 4 percent..."

And from http://www.history.navy.mil/library/onl ... rowler.htm -- "In 1996, flight testing was suspended when problems with the Super Hornet's engines caused the aircraft to be grounded. The Super Hornet fleet was grounded a second time in 1998 when engine problems resurfaced."

So much for that idea...
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Unread post06 Mar 2013, 07:58

RM-12 had a few problems during development, Some resonance phenomena causing fatigue and some low thrust during quick start missions, but all problems were ironed out prior to IOC and the engine have functioned quite nice in service.

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Unread post06 Mar 2013, 23:05

Engine crack that grounded F-35 traced to thermal creep 06 Mar 2013 Zach Rosenberg

http://www.flightglobal.com/news/articl ... ep-383136/

"Bennett Croswell, president of Pratt & Whitney's military engine division, says a problem with F135 engines that grounded the Lockheed Martin F-35 is due to thermal creep, and is unlikely to affect the aircraft further as it returns to flight status.

The issue was a crack in a third-stage turbine blade on a single engine. As a precaution, the US military grounded all F-35 aircraft until a cause was discovered.

"During [an] inspection we found about 1/6-inch (4.2mm) crack on the turbine blade," says Croswell. "We felt we could continue to fly, and we took that recommendation to the (joint programme office), but on consultation with them we both came to the conclusion it was safer to suspend operations."

Thermal creep from high-temperature, high-intensity testing was found to be the cause of the crack. The engine the tenth engine built, powers the second F-35A, was tested extensively at supersonic speeds and low altitudes, generating significant more heat than expected.

"It was operating at levels 4X an operational mission, and 4X of levels we had qualified the engine for," says Croswell. "That was very good news, you don't want something like high-cycle fatigue or low-cycle fatigue." The issue is not expected to impact operational aircraft for months or years, depending on how the aircraft are flown...."
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Unread post08 Mar 2013, 01:36

So what might be the remediation for this particular engine? Since Pratt has decided that thermal creep was responsible for the crack, does that mean all LPT blades will be replaced? What other parts might be susceptible to the effects of thermal creep?
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Unread post08 Mar 2013, 15:48

So what might be the remediation for this particular engine?
Well, for sure they will study this engine from stem to stern since it did go 4x the spec. At the very least, this blisk will be replaced.
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